client.py

import socket
import struct
import pickle

localhost_with_port_9000 = ( "127.0.0.1", 9000 )

# Recall:
# header size is 2 * 4 Unsigne Int = 8 Bytes
# header_rawbyte = struct.pack("!2I", *header), defined in server code

HEADER_SIZE = 8


with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as client_socket:

    client_socket.connect( localhost_with_port_9000 )

    print(f"connect to {localhost_with_port_9000} ...")

    # read buffer for client
    buffer = bytes()

    while True:

        # receive data bytes on network from server
        raw_bytes = client_socket.recv(512)

        if raw_bytes:

            buffer += raw_bytes

            while True:

                if len(buffer) < HEADER_SIZE:
                    print("\n Keep reading until full rawbytes of header is read \n")
                    break

                # decode and recover header from rawbytes
                header = struct.unpack('!2I', buffer[:HEADER_SIZE])

                # definition of header
                # first field is id
                # second field is size of payload
                id, payload_size = header

                if len(buffer) < (HEADER_SIZE + payload_size):

                    print("\n Keep reading until buffer size is long enough to decode payload \n")
                    break

                payload_rawbyte = buffer[HEADER_SIZE: HEADER_SIZE+payload_size ]

                # decode and recover data from payload rawbytes
                data = pickle.loads( payload_rawbyte )

                print("\nDecode is successful")
                print(f"id = {id}")
                print(f"data = {data} \n")

                if data.get("demand", "") == "quit connection":
                    print("\n Client get quit connection message from server \n")
                    exit(0)

                # discard old data in buffer
                buffer = buffer[HEADER_SIZE+payload_size:]